Seismic studies reveals paleochannels that dissected the Rio Grande do Sul coastal zone. Two paleochannels systems were established in the Patos Lagoon area. The channel filling of the younger system is Holocene. It is related to the last marine regression of the Pleistocene, corresponding to the oxygen isotope stage 2. The incision and filling of the older system is related to the previous regressive-transgressive event, corresponding to the oxygen isotope stages 6-5. The paleodrainage paths were connected with those previously recognized on the adjacent continental shelf. Landwards, the paleodrainage lines can be linked with the present courses of the Camaquã and Jacuí rivers. The paleodrainage network recognized on the coastal zone represents a river-shelf system, linking the drainage basin to the depositional settings on the marginal basin, bypassing the continental shelf exposed during a forced regression event. The bypassing discharge of the younger system fed delta systems installed on the shelf edge during the sea level lowstand that lasted until the end of the last glaciation. The last transgression drowned the incised drainage, infilling it and closing the inlets formerly existing between the Patos Lagoon and the Atlantic Ocean. The incised paleodrainage herein considered may have played an important role on the basin-margin architecture, facies distribution and accommodation during the Quaternary sea level oscillations.
seismic survey; paleodrainage network; Patos Lagoon
